["Non naturals" in Islamic medicine].

"Non naturals," which appear frequently in the history of Western medicine, means things not controlled by human nature, contrary to natural components of a body. It covers such a wide range of factors as physiological or psychological things, and the external envionment. Generally, these are classified into six categories; ambient air, food and drink, exercise and rest, sleep and wakefulness, excretion and retention, and the passions of soul. In medieval times the knowledge of these "six non naturals" constituted a kind of hygiene or regimen. People cannot avoid the effects of these elements in their lifetime, so physicians were required to learn about them not only to treat diseases but to preserve health and to prevent diseases. This became so common that it was included in the curriculum of medical schools. Although these factors were already known to have an effect on the health of humans in the early stage of Greek medicine, it took a long time to be formed into the theory of "six non naturals." Its origin can be traced back to Galen's "Ars medica," but he does not use the name "non naturals." With the later development of medicine in the Islamic world, which received Greek medicine through translation, the number and the contents of related factors differ from author to author. Moreover, they use different names; few authors use the name "non naturals." It seems that "six non naturals" had not been established as theory until the later stage of the history of medicine in Islam.